When Kaneki crosses over into the 'Persona' universe, a cool plot twist is that his split personality as a ghoul is somehow related to the concept of personas. So, his struggle with his different selves becomes intertwined with the way personas work in that world. It's not just a simple crossover but a deep exploration of Kaneki's character through a different lens.
In some crossovers, like the one with 'Bleach', a really creative plot twist is when Kaneki's kagune somehow gets linked to a Hollow's power. It completely changes the power dynamics and makes for some intense battles. The idea that his ghoul nature could be combined with Hollow abilities in such a way was unexpected and exciting.
In a crossover with the 'Harry Potter' world, a creative plot twist is that Kaneki's ghoul powers are mistaken for some kind of dark magic. But instead of being persecuted, he uses his powers to protect Hogwarts from a new, unknown threat. This flips the typical 'outsider' narrative and gives Kaneki a new role within the wizarding world, leading to some really interesting interactions with the Hogwarts students and staff.
One interesting plot twist could be the ghouls in the Attack on Titan world. Imagine if ghouls were hidden among the titans. They could feed on the bodies of dead titans or even on the soldiers without being detected at first. Another could be the Ackermans having some sort of connection to the ghoul powers. Maybe their enhanced strength is related to a dormant ghoul gene. And a third could be the Scouts finding a way to use ghouls' kagune to fight the titans more effectively, like creating weapons out of kagune material.
One interesting plot twist could be a character from 'Supernatural' getting the kagune power from 'Tokyo Ghoul'. For example, Dean suddenly having a rinkaku kagune and having to learn how to control it while still hunting demons. It would add a whole new layer to his character as he struggles with this new, inhuman power.
One great Tokyo Ghoul Kaneki crossover fanfiction is the one where he crosses over with the world of 'Attack on Titan'. It's really interesting to see how Kaneki's ghoul abilities interact with the Titans. The author does a great job of creating a believable scenario where the two worlds collide.
In a fanfiction where Kaneki is overpowered, he could have the power to heal the rift between humans and ghouls in a more radical way. He could use his extreme strength to force the humans to accept the existence of ghouls and also make the ghouls understand the importance of not preying on humans. His overpowered abilities would be like a shockwave that shakes the very foundation of the existing relationships and rebuilds them in a more positive way. For instance, he could create a safe zone where both humans and ghouls can live together without fear, and his overpowered presence would ensure that no one breaks the peace.
A cool plot twist could be a ghoul - Titan hybrid. Imagine a Titan with the regenerative abilities of a ghoul. This would pose a whole new level of threat to the characters from both universes. Also, the idea of the ghouls' coffee being a valuable resource in the Attack on Titan world could be an interesting twist. Since coffee is so important to ghouls, it could have some unforeseen effects on the Titans or the people in that world.
One interesting female Kaneki fanfiction could be one where she forms an unexpected alliance with a group of ghouls from a different territory. In this story, she might use her unique perspective as both human and ghoul to bridge the gap between different ghoul factions. It could explore her internal struggle in a new light as she tries to maintain her humanity while also fitting into the ghoul world.
One possible fanfiction could be where Kaneki, after fully mastering his ghoul powers, becomes a sort of protector in the ghoul world. He could use his strength to keep the balance between humans and ghouls, defying the traditional enmity. He might be able to create new rules that both sides can abide by, making the world a more harmonious place for both species.
Perhaps a plot twist where the Mist from Percy Jackson's world starts to affect Tokyo Ghoul. The Mist could make humans in Tokyo see ghouls as something completely different, like mythical creatures from their own Japanese folklore. This would not only change how the humans in Tokyo Ghoul react to ghouls, but also how the ghouls themselves perceive their place in the world and their relationship with humans.
Well, perhaps a major plot twist could be that the CCG (Commission of Counter Ghoul), which is supposed to be against ghouls, has been secretly working with some ghouls for their own ulterior motives. This would be a huge shock as it goes against everything they are known for. Also, there could be a twist where a ghoul's kagune (their weapon - like organ) mutates in a way that gives them an unexpected advantage or disadvantage.
If Kaneki turns into a baby in fanfiction, it could be a way to explore his character in a new light. Maybe he retains some of his memories from his previous form, but is unable to communicate them clearly. This could lead to a lot of misunderstandings and new adventures. Also, it could be a chance for the author to develop new relationships for Kaneki, as a baby he would be more vulnerable and dependent on others.